IUBio

Help Blood Groups?

I Pierce sandj at pierce.u-net.com
Sat Dec 14 16:41:33 EST 1996


Can anyone clarify this for me?

In the ABO system of blood groups a group A person has the A antigen
(agglutinogen) on the surface of their erythrocytes and the anti-B
antibody (agglutinin) in their plasma.
Normally you would not expect someone to possess an antibody against
something they had not been exposed to (except in the case of passive
immunity). Therefore it would seem odd that a person with type A blood
should already possess anti-B. I have always asssumed that the reason
for this is that intestinal bacteria also display similar antigens
(cross reacting) on their surface (since they are fairly common
carbohydrates) and that we therefore develop antibodies to those
antigens which we don't possess, early in life. Following the logic of
this we wouldn't make anti-A because of self tolerance. Is this
actually true?

I'm now wondering about rhesus blood groups. Presumeably the rhesus
antigen (or anything like it) is not found in intestinal bacteria
since a rhesus negative woman isn't usually sensitised by a rhesus
positive foetus until the end of her first pregnancy. Any thoughts?

Simon




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